A daily vitamin D intake of 1000–4000 IU (25–100 micrograms) should be enough to ensure optimal blood levels for most people.

Bottom Line: Blood levels in the range of 20–30 ng/ml are usually considered sufficient. The safe upper limit is considered to be about 60 ng/ml, but people with symptoms of toxicity usually have levels above 150 ng/ml.

The main consequence of vitamin D toxicity is a buildup of calcium in the blood, called hypercalcemia (25).

Early symptoms of hypercalcemia include nausea, vomiting, diarrhea, constipation and weakness (26).

Excessive thirst, an altered level of consciousness, high blood pressure, calcification in the kidney tubes, kidney failure or hearing loss may also develop (4, 27).

Hypercalcemia caused by regularly taking high amounts of vitamin D supplements may take a few months to resolve. This is because vitamin D accumulates in body fat, and is released into the blood slowly (4).

Keep in mind that these are just hypotheses, but it may be wise to make sure you are getting enough of these nutrients if you are going to supplement with vitamin D.

Bottom Line: If you are supplementing with vitamin D, then it may be important to also ensure sufficient intake of vitamin A, vitamin K and magnesium. These may reduce the risk of adverse effects from a higher vitamin D intake.